1. Field of the Invention
The present invention relates, in general, to a scanning arrangement in a scanner and incorporating a scan element which is capable of the repetitive high-speed scanning of indicia having parts of different light reflectivity; for example, such as barcode symbols, and more particularly, pertains to the operation of a scanning arrangement of the type which, at high scanning speeds, will enable the scanning of indicia in variable and specified omni-directional scanning patterns.
In accordance with specific aspects, the invention is directed to the provision of novel scanning methods and apparatus for omni-directionally scanning indicia through the use of a single scan element, especially such as a resonant asymmetric scan element, operating in at least two different frequency modes creating a precessing lissajous pattern so as to provide an at least 1/3 omni-directional scan of the indicia.
As contemplated pursuant to another aspect of the invention, the variable omni-directional scanning pattern is attained through control over the electrical energy input to a read-start device for activating the scan element of the scanner for vibratory motion between first and second pairs of scan end position, in which the energy input is controlled and varied in a manner so as to enable the scan element to implement the aforementioned omni-directional scanning patterns over the indicia.
According to a specific feature of the invention, an omni-directional scanning pattern is realized in that a double lissajous pattern is implemented by a single scan element through the combining of a fast lissajous pattern with a slower lissajous pattern and periodically changing between the two lissajous patterns through control over the electrical energy input such that there is obtained an omni-directional scanning pattern without the necessity of having to utilize an additional motor in the scanning arrangement.
Additionally, as contemplated by another concept of the invention, the electrical energy input to the read-start means for imparting the vibratory movements to the scan element of the scanning arrangement causes the relative amplitudes between the different scanning directions of the scan element to be varied, such as in sinusoidal modes, so as to allow for decoding of indicia in any orientation which; in effect, will provide a full omni-directional scanning pattern to allow presentation in any orientation of the indicia.
The foregoing varying modes of scanning to attain the different and varying types of omni-directional scanning patterns is readily attained through the use of currently existent scanning devices, particularly such as by means of a resonant asymmetric scan element, through controlling the electrical energization frequency and/or intensity supplied to the read-start device for the scan element employed in the scanning arrangement.
The utilization of laser scanning devices for the scanning or reading of information provided on a target; such as a package or sale item, is well known in this particular technology and has found wide acceptance in commerce. In this connection, various types of laser scanning devices incorporate scanning heads which house optical reading systems, such as barcode readers, for the reading of information or barcode symbols on targets which are scanned by a laser beam projected from the barcode reader. In general, such laser scanning devices; especially those in the type of barcode readers, are widely employed in industry, such as manufacturing, shipping, and in retail commerce and; for example, may be permanently incorporated in the structures of check-out counters of supermarkets, whereby the items of merchandise having the barcode symbols imprinted thereon or applied thereto are passed over a fixed barcode reader located beneath the counter surface so as to provide a record for the merchant of the merchandise being purchased by a consumer, and concurrently a readout (and possibly a printed record) for the consumer.
Alternatively, the barcode reader or laser scanning device may also be constituted of an optical scanner unit which is fixedly mounted on a stand extending above a support platform or countertop on which the merchandise may be arranged; or in many instances of utilization, pursuant to a preferred embodiment of the invention, may be in the form of a miniature, lightweight and gun-shaped device having a pistol grip, and which the activated device is normally passed over the barcode symbol which is imprinted on a sale item or target at some short distance therefrom so as to enable scanning of the information provided by the barcode symbols.
2. Discussion of the Prior Art
Various optical readers and optical scanning systems have been developed heretofore for reading barcode symbols appearing on a label or on the surface of an article. The barcode symbol itself is a coded pattern of indicia comprises of a series of bars of various widths spaced apart from one another to bound spaces of various widths, the bars and spaces having different light-reflecting characteristics. The readers and scanning systems electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumerical characters that are intended to be descriptive of the article or some characteristic thereof. Such characters are typically represented in digital form and utilized as an input to a data processing system for applications, in point-of-sale processing, inventory control, and the like. Scanning systems of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,369,361; 4,387,297; 4,409,470; 4,760,248; and 4,896,026, all of which have been assigned to the same assignee as the instant application.
As disclosed in some of the above patents, one embodiment of such a scanning system resides, inter alia, in a hand-held, portable laser scanning head supported by a user, which is configured to allow the user to aim the head, and more particularly, the light beam or laser beam projected therefrom, at a target and a symbol which is to be read.
The light source in a laser scanner is typically a gas laser or semiconductor laser. The use of semiconductor devices, such as a laser diode, as the light source in scanning systems is especially desirable because of their small size, low cost and low power requirements. The laser beam is optically modified, typically by a lens, to form a beam spot of a certain size at the target distance. It is preferred that the beam spot size at the target distance be approximately the same as the minimum width between regions of different light reflectivity, i.e., the bars and spaces of the symbol.
Barcode symbols are formed from bars or elements that are typically rectangular in shape with a variety of possible widths. The specific arrangement of elements defines the character represented according to a set of rules and definitions specified by the code or "symbology" used. The relative size of the bars and spaces is determined by the type of coding used, as is the actual size of the bars and spaces. The number of characters per inch represented by the barcode symbol is referred to as the density of the symbol. To encode a desired sequence of characters, a collection of element arrangements are concatenated together to form the complete barcode symbol, with each character of the message being represented by its own corresponding group of elements. In some symbologies a unique "start" and "stop" character is used to indicate where the barcode begins and ends. A number of different barcode symbologies exist. These symbologies include UPC/EAN, Code 39, Code 128, Codabar, and Interleaved 2 of 5.
For purpose of discussion, characters recognized and defined by a symbology shall be referred to as legitimate characters, while characters not recognized and defined by that symbology are referred to as illegitimate characters. Thus, an arrangement of elements not decodable by a given symbology corresponds to an illegitimate character(s) for that symbology.
In order to increase the amount of data that can be represented or stored on a given amount of surface area, several new barcode symbologies have recently been developed. One of these new code standards, Code 49, introduces a "two-dimensional" concept by stacking rows of characters vertically instead of extending the bars horizontally. That is, there are several rows of bar and space patterns, instead of only one row. The structure of Code 49 is described in U.S. Pat. No. 4,794,239, which is hereby incorporated by reference.
A one-dimensional single-line scan, as ordinarily provided by hand-held readers, has disadvantages in reading these two dimensional barcodes; that is, the reader must be aimed at each row, individually. Likewise, the multiple-scan-line readers produce a number of scan lines at an angle to one another so these are not suitable for recognizing a Code 49 type of two-dimensional symbols.
In the scanning systems known in the art, the light beam is directed by a lens or similar optical components along a light path toward a target that includes a barcode symbol on the surface. The scanning functions by repetitively scanning the light beam in a line or series of lines across the symbol. The scanning component may incorporate a drive or scanning motor adopted to either sweep the beam spot across the symbol and trace a scan line across and past the symbol in a high-speed repetitive mode, or scan the field of view of the scanner, or do both.
Scanning systems also normally include a sensor or photodetector which functions to detect light reflected from the symbol. The photodetector is therefore positonied in the scanner or in an optical path in which it has a field of view which extends across and slightly past the symbol. A portion of the reflected light which is reflected off the symbol is detected and converted into an electrical signal, and electronic circuitry or software decodes the electrical signal into a digital representation of the data represented by the symbol that has been scanned. For example, the analog electrical signal from the photodetector may typically be converted into a pulse width modulated digital signal, with the widths corresponding to the physical widths of the bars and spaces. Such a signal is then decoded according to the specific symbology into a binary representation of the data encoded in the symbol, and to the alphanumeric characters so represented.
The decoding process in known scanning systems usually work in the following way. The decoder receives the pulse width modulated digital signal from the scanner, and an algorithm implemented in software attempts to decode the scan. If the start and stop characters and the characters between them in the scan were decoded successfully and completely, the decoding process terminates and an indicator of a successful read (such as a green light and/or an audible beep) is provided to the user. Otherwise, the decoder receives the next scan, performs another decode attempt on that scan, and so on, until a completely decoded scan is achieved or no more scans are available.
Such a signal is then decoded according to the specific symbology into a binary representation of the data encoded in the symbol, and to the alphanumeric characters so represented.
Laser scanners are not the only type of optical instrument capable of reading barcode symbols. Another type of barcode reader is one which incorporates detectors based upon charge coupled device (CCD) technology. In such readers, the size of the detector is larger than or substantially the same as the symbol which is to be read. The entire symbol is flooded with light from the reader, and each CCD cell is sequentially read out to determine the presence of a bar or a space. Such readers are lightweight and easy to use, but require substantially direct contact or placement of the reader on the symbol to enable the symbol to properly read. Such physical contact of the reader with the symbol is a preferred mode of operation for some applications, or as a matter of personal preference by the user.